Composite structures are desirable in many industries for many applications. The aerospace industry, for example, uses composite structures extensively because, among other desirable attributes, composites have high strength-to-weight ratios. Because of the ever increasing use of composite structures throughout industry, manufacturers are continually searching for better and more economical ways of fabricating composite structures.
Composite structures applied to the exterior of ships and aircraft can experience significant degradation and damage due to their exposure to erosion and environmental attack. In this regard, such structures are constantly subjected to oxidation, moisture, fouling, salt-spray, UV radiation, chemicals, and high and low temperatures, among other things, that can cause such structures to experience significant degradation and damage over time. As a consequence, such structural components are often constantly repaired or replaced to prevent the possibility that a given vessel or aircraft will be damaged permanently, if not destroyed.
To attempt to prevent the damage caused by fatigue and environmental exposure on such composite components, a variety of coating agents and methods of applying the same to such components have been developed to improve their durability. Thermal spraying is one method for applying thermoplastic polymers to a surface. Thermal spraying comprises insertion of feed stock particles, typically of a polymer-like material, into a high-energy heat source that propels the particles, while in a liquid or semi-liquid state, onto the surface of the component sought to be protected. Once propelled onto the surface sought to be protected, the particles fuse together and form a coating on the surface.
High performance thermoplastics offer the potential of a higher wear resistant and lower permeability barrier material as compared to conventional coatings. Thermoplastic coatings on a variety of substrates have been demonstrated using thermal spray techniques. However, when a high melt temperature, high performance thermoplastic such as liquid crystal polymer (LCP) is thermally sprayed on a composite with moderate temperature resistance, out-gassing of moisture and volatiles from the composite substrate can occur which can degrade the structural morphology of the coating. One solution to this problem, described in U.S. Pat. No. 6,174,405 issued to Clarke et al., involves thermally spraying a thermoplastic such as LCP on a metal mold, commonly referred to as a tool. While the coating is still on the tool, a prepreg or wet lay-up of the composite is applied directly on the thermoplastic-coated tool. The composite/coating/tool assembly is then oven/autoclave cured, and, when curing is completed, the thermoplastic-coated composite structure is removed from the tool.